CHAP. VIII. ON CLEISTOGAMIC FLO WEES. 339 



devoured by birds or other enemies. But this advan- 

 tage is accompanied by the loss of the power of wide 

 dissemination. No less than eight of the genera 

 in the list at the beginning of this chapter include 

 species which act in this manner, namely, several 

 kinds of Viola, Oxalis, Vandellia, Linaria, Commelina, 

 and at least three genera of Leguminosae. The seeds 

 also of Leersia, though not buried, are concealed in 

 the most perfect manner within the sheaths of the 

 leaves. Cleistogamic flowers possess great facilities 

 for burying their young ovaries or capsules, owing to 

 their small size, pointed shape, closed condition and 

 the absence of a corolla ; and we can thus understand 

 how it is that so many of them have acquired this 

 curious habit. 



It has already been shown that in about 32 out of 

 the 55 genera in the list just referred to, the perfect 

 flowers are irregular ; and this implies that they have 

 been specially adapted for fertilisation by insects. 

 Moreover three of the genera with regular flowers are 

 adapted by other means for the same end. Flowers 

 thus constructed are liable during certain seasons to 

 be imperfectly fertilised, namely, when the proper 

 insects are scarce ; and it is difficult to avoid the 

 belief that the production of cleistogamic flowers, 

 which ensures under all circumstances a full supply 

 of seed, has been in part determined by the perfect 

 flowers being liable to fail in their fertilisation. But 

 if this determining cause be a real one, it must be of 

 subordinate importance, as four of the genera in the 

 list are fertilised by the wind ; and there seems no 

 reason why their perfect flowers should fail to be 

 fertilised more frequently than those in any other 

 anemopliilous genus* In contrast with what we here 

 see with respect to the large proportion of the perfect 



